fix(extension): don't abort hub tasks when configure precedes execute

[apakkhalin-sudo]

Fixes #570

Problem

Every task sent through the MCP server fails instantly with "Task aborted" whenever any of LLM_BASE_URL / LLM_API_KEY / LLM_MODEL_NAME is set — even when those values are identical to the extension's saved settings. The extension popup works fine, and the hub makes zero network requests before failing.

Root cause

packages/mcp attaches a config object to every execute message when LLM env vars are set. In the hub, useHubWs.onExecute then does:

if (incomingConfig) {
  await configure({ ...config, ...incomingConfig } as ExtConfig)
}
const result = await execute(task)

configure() calls setConfig() in useAgent, which re-renders and re-runs the useEffect([config]). That effect's cleanup disposes the current agent and installs a new one — but execute() resolves agentRef before React commits the new agent, so the task starts (or is about to start) on the agent being disposed. dispose() fires its AbortController, and PageAgentCore returns the literal "Task aborted".

Observable in the hub tab's console on every MCP run: init → Disposing PageAgent... → dispose.

Fix (in useAgent.configure())

1. Value-equal config → skip the rebuild. If the merged config equals the current one (the common MCP case, since the env config usually mirrors saved settings), don't setConfig at all — no re-render, no dispose. Storage writes still happen.
2. Changed config → await the rebuild. configure() now resolves only after the [config] effect has installed the new agent, so callers never execute() on an agent whose dispose is already scheduled.

Verification

• npm run typecheck, npm test (17/17), npm run lint, npm run build:ext all pass.
• Runtime-verified the equivalent behavior end-to-end: with config no longer triggering a rebuild before execute, MCP execute_task completes successfully through hub → extension → LLM → page (previously 100% instant abort).

🤖 Generated with Claude Code

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}